A study suggests that photosynthetic eukaryotes may have emerged around 1.9 billion years ago in freshwater habitats. Eukaryotes are thought to have evolved the capacity for photosynthesis through a process called endosymbiosis, in which a protist host encapsulated a photosynthetic cyanobacterium. The first such endosymbiotic event gave rise to the group called archaeplastida, which includes glaucophytes, red algae, green algae, and land plants. The timing and circumstances of the first endosymbiotic event and the dates of divergence of the major subgroups within archaeplastids remain unestablished, partly due to incomplete phylogenies and gaps in the fossil record. Patricia Sánchez-Baracaldo and colleagues performed molecular clock and phylogenomic analyses on two datasets, comprising 49 cyanobacterial genomes and 119 taxa, including cyanobacteria and photosynthetic eukaryotes, to estimate the age of the primary endosymbiotic event as well as subgroup divergence times. Analysis revealed that the cyanobacterium Gloeomargarita, the closest relative of archaeplastids, likely diverged from its sister group, the chloroplast lineage, around 2.1 billion years ago in freshwater. Further, the common ancestor of archaeplastids likely became established around 1.9 billion years ago, marking the plausible origin of the first photosynthetic eukaryote. Over the next 1 billion years, major groups of modern photosynthetic eukaryotes likely diversified in freshwater habitats. The findings bolster fossil evidence and help unravel the origins of photosynthetic eukaryotes, according to the authors.
Article #16-20089: "Early photosynthetic eukaryotes inhabited low-salinity habitats," by Patricia Sánchez-Baracaldo, John Raven, Davide Pisani, and Andrew Knoll.
MEDIA CONTACT: Patricia Sánchez-Baracaldo, University of Bristol, UNITED KINGDOM; tel: +44-0117-331-7269, +44-7985967241; e-mail: <email@example.com>